Boletín de aludes

Flathead Range & Glacier NP

Flathead Avalanche Center
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Peligro de aludes

Sun
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Large natural avalanches have occurred during the last week.  Watch for dunes of drifted snow beside ridges, below saddles, and in gullies.  Move to a sheltered or less steep area if the snow cracks around your feet or machine.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Northeast winds during this week's Arctic intrusion have built drifts of snow in abnormal locations, including low elevations. This loading pattern has produced recent large natural avalanches, and human triggering is still possible.  Today, southwest winds will drift snow onto typically leeward terrain and begin to build soft slabs. These features will be the thickest and most dangerous near and below ridgelines and saddles, around prominent terrain features, and in cross-loaded gullies. Cracking indicates instability and should direct you to a more sheltered slope or lower-angle terrain.  

    Observers have reported hard and supportable slabs in the most wind-exposed areas.  Hard slabs are particularly difficult to manage as they do not readily show signs of instability, can fracture above you, and often propagate wider than expected. They're also not much fun to ride on, so it's best to adjust your route if your skis or machine suddenly start riding on top of a firm surface that feels hollow or drum-like.

    Loose Dry: Several days of bitterly cold temperatures have left cold, loose snow on the surface at all elevations and aspects unaffected by the recent northeast winds. Today’s warming temperatures and periods of sunshine may initiate loose avalanches on slopes facing NW-SW-SE. Snow falling from tree branches or peeling off rock faces indicates instability and directs you to a different aspect, not being warmed by solar radiation. You could trigger a sluff on steep slopes harboring loose snow, especially if it rests on a crust. Manage your sluff and limit time spent above terrain traps and cliff bands.

    (2/24/2023)

    We decided to turn it around pretty shortly after augering into these drifts.

    Photo: RVM

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    This week, rapid loading from new snow and high winds initiated numerous slides on weak layers buried deep in the snowpack. Most of the avalanche activity associated with these layers has been on shady aspects at mid and upper elevations. Natural avalanche activity has tapered off, and it is becoming more difficult for the weight of a rider or their snowmachine to trigger one of these slides. A surface avalanche or cornice fall has the potential to trigger a deeper slide and increase the consequences.

    Digging into the snowpack is the only way to identify if a slope contains one of these weak layers. The easiest way to deal with this problem is through effective terrain management - avoid traveling on and below steep slopes. Steer clear of likely trigger points, including convexities and areas where the snowpack is thin and rocky.

    (2/24/2023)

    D3 debris from a hard slab avalanche on a SE facing path.

    Photo: md

Avalanche Discussion

Yesterday (Friday) the Arctic oppressor lessened its grasp on the advisory area and riders crept back into the terrain to see what soft snow they could salvage. Conditions reportedly ranged from unrideable lunar landscapes, to pleasant sheltered powder turns. Observations also included many recent natural avalanches ranging from small to very large that failed during this week’s impressive snowfall and wind-loading. 

Warming temperatures and clearing skies will welcome riders back to the mountains today. However, it’s important to take some time to re-introduce yourself to the snowpack. A lot has changed in the last week. Roughly 1-2 feet of snow and 3-5 inches of SWE blanketed the advisory and was rebuffed by winds shifting from northeasterly to southwesterly. The natural cycle is behind us, but riders can still trigger lingering instabilities. Uncertainty is high following a couple days of intolerable temperatures and limited observations. Variability is also likely to be high due to this week’s combination of snow and wind.

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